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06-14-2013, 01:56 PM   #1
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Pentax Primes fit 645

I happened to be looking at the Pentax Imaging web site and this Forum and was surprised to see that the 31mm, 43mm, and 77mm primes I have will work on a 645. Is this true? Is there a shortcoming to using this combination? I'm curios because I'm looking to moving up to a camera that would offer me more. The 645 looks like the camera to do that. I also have a SMC FA 100mm F2.8 macro (the tank not the newer one) and an AF540. I also have the DSLR kit lens I got with my K10D, which I still have and a K-5 that I broke the Viewfinder Diopter Slide and the rubber and plastic framed eyecup. I'm in the process of getting it fixed.

Is the expense of the 645 worth it? Or should I wait until the new DSLR comes out.

I've been using Pentax's since my MX. I'd like to remain loyal but I'm wondering if there's something better out there.

06-14-2013, 02:16 PM   #2
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That's not quite true. 6X7 can mount onto 645, 645 unto K, K unto Q. Can't put K onto 645 sadly. (Well, I suppose you could, but it'd be a circle with black all around it)

That said, the lenses Pentax makes for the 645D are spectacular.

In regard to the expense being worth it, that really depends what you're doing. If you want to shoot sports, a MF camera isn't going to be too great for that. If you shoot landscape for a living though, I suppose it's worth it. If you're just an enthusiast, I'd recommend waiting for the next top-tier Pentax camera. (Be it a 24MP APS-C or a 36MP FF)
06-14-2013, 06:43 PM   #3
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the biggest problem is the flange on the pentax 645D which is 70.87mm Vs the K mount which has a flange of 45.46mm - this means it would be only possible to use K mount lenses for extreme macro photography on the 645D. Infinity focus would be impossible to achieve, unless you added lenses to make up for the differential in the flange distance.

According to my tests on my optics bench the FA limited lenses have an imaging circle that can just cover the 44X33mm sensor of the 645D*, but with the exception of the FA31 I don't think the FA43 and FA77 would only produce usable images until f/4~f/5.6.

* I did these tests keeping the standard 45.46mm K mount flange. As with most lenses, the fall off gets pretty bad at the extremities of the imaging circle and resolution drops off quite a bit as well. But theoretically if Pentax made a mirrorless 645 camera with the roughly same flange as the K mount, theoretically you could get away with using the FA31 limited on it.
06-14-2013, 07:09 PM   #4
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QuoteOriginally posted by Digitalis Quote
a mirrorless 645 camera
Talk about a niche camera!

06-14-2013, 07:59 PM   #5
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QuoteOriginally posted by dadipentak Quote
Talk about a niche camera!
I agree, but pentax has an interest in mirrorless ( take a look at the Pentax Q) and Ricoh seems to be putting some capital into development of mirrorless camera systems. Though there would be one significant hurdle with a mirrorless 645 - fall off and lens shading, which can be really problematic with wide angle lenses with short back focus*. astigmatism is also more problematic with short flanges than it is with longer ones because of the proximity of the lens to the sensor.

* This is rather evident when I have used my Leica M9 with a non leica wideangle lens like the Zeiss Biogon 28mm f/2.8 or the Voigtlander Heliar 12mm f/5.6. And I have seen this problem occur with Sony NEX cameras as well. Lens shading is when you get pink/green corners in an image and it can be difficult to correct.
06-17-2013, 07:52 PM   #6
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QuoteOriginally posted by dadipentak Quote
Talk about a niche camera!
Well, actually, it might be a useful niche, come down to it. My oldest-time Pentaxianness was all about shooting the 6x7: if I wanted to do any kind of high res photography with medium format digital, (ie, on a tripod) ...eliminating that mirror mechanism might be a worthwhile thing to deal with. (Even if in my case I'd want a nice big EVF if not a focusing hood to throw over my head. I'm not big on mirrorless cause I like to see the light and all, and it's nothing MLU and Live View couldn't do, but if my thing were landscape or macro, or other things, it might be worth not paying for or schlepping around the prism and mechanism. Put a leaf shutter lens on that baby, even, I could see people liking it.

Last edited by Ratmagiclady; 06-17-2013 at 07:58 PM.
06-18-2013, 05:08 AM   #7
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QuoteOriginally posted by Ratmagiclady Quote
Well, actually, it might be a useful niche
Ok I see where you're going with that.

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